This application relates generally to the field of Lasers and Laser Amplifiers. More specifically, the application relates to solid state laser amplifiers in the form of a slab which are pumped optically by lamps and where the laser beam enters through a Brewster angle facet and experiences multiple face to face bounces due to total internal reflection before exiting through the same face as that the beam entered.
Generally, lamp driven slab lasers have existed for many years. The prior art is exemplified by General Electric's design of a Krypton arc lamp driven, face pumped, face to face multi-bounce, total internal reflection (TIR) Nd:Yag (Neodymium doped Yttrium Aluminum Garnet) slab. In General Electric's design, the Nd:Yag crystal was face pumped with Krypton arc lamps. These particular designs achieved a conversion efficiency (laser power out divided by electrical power in) of ˜4% with an output that reached several Kilowatts. In this design, Krypton arc flash or arc lamps (consisting of cerium doped quartz envelopes) discharging a spectrum of blackbody and line emission photons that were subsequently reflected as evenly as possible onto the adjacent faces of the Neodymium doped Yitrium Aluminum Garnet slab. This gain element selectively absorbed portions of this energy. This energy excited the Neodymium atoms into an elevated energy state from which the laser beam was generated or amplified.
Later versions incorporated Diode laser pump sources to increase efficiency and architectural simplicity (by producing only a particular frequency of photonic energy that is highly absorbed by the doped Yag). Still later versions employed Nd doped Ytterbium Vanadate (YbVO4) as the gain medium. Such systems have become the standard with the limitation being the maximum size that YAG, Vanadate or gain crystals can be fabricated. U.S. Pat. Nos. 3,633,126 and 3,631,362 discuss related technologies.
The previously mentioned diode pumped systems have demonstrated system efficiencies of 10%, with efficiencies that might even approach 25% in ideal circumstances, but at a high financial cost, with the breakdown being approximately 50% efficiency for the diode pump lasers, 65% efficiency for the Nd:VO4, for Nd:YAG the efficiency has been about 50% conversion to the 1.064 micron radiation, and subsequent beam clean-up reducing the system output efficiency to as low as 10% with the overall efficiency of well-designed systems being about 25%. The current upper limit to the output power has been demonstrated with both Ceramic Yag slabs that were fiber edge pumped and with face pumped versions, both of which were built chiefly by Northrop Grumman. Their system demonstrated an output of 25 kW (KiloWatt) per laser head, with an efficiency of ˜50% for the Diode pump lasers, and a conversion efficiency of ˜50% in the Nd:Yag slab for an output efficiency at approximately 25%.
The limiting efficiency for the existing lamp pumped designs are primarily in two areas. First is the inefficiency due to the fact that the emitting spectrum from the pump lamps typically does not match the excitation spectrum of the laser crystal material. Second is in the inefficiency of the beam extraction from the gain material due to having the beam pass through no more than twice and incompletely fill the gain material. These drawbacks have interfered with potential practical applications of the slab laser concept.